Coated cutting tool

ABSTRACT

A coated cutting tool having a substrate and a surface coating, wherein the coating includes a Ti(C,N) layer of at least one columnar fine-grained MTCVD Ti(C,N) layer with an average grain width of 0.05-0.2 μm and an atomic ratio of carbon to the sum of carbon and nitrogen (C/(C+N)) contained in the MTCVD Ti(C,N) layer is in average 0.50-0.65.

RELATED APPLICATION DATA

This application is a reissue of U.S. Pat. No. 9,956,667, filed Dec. 11,2015, which claims the benefit of § 371 National Stage Application ofPCT International Application No. PCT/EP/062351 filed Jun. 13, 2014claiming priority of EP Application No. 13172154.0, filed Jun. 14, 2013.

TECHNICAL FIELD

The present invention relates to a coated cutting tool for chip formingmachining of metals comprising a substrate having a surface coated witha chemical vapor deposition (CVD). In particular the present inventionrelates to a coated cutting tool having a CVD coating comprising atleast one fine-grained titanium carbonitride.

BACKGROUND

Cutting tools for chip forming machining of metals, such as round tools,i.e. end mills, drills, etc., and inserts, made of durable materials,such as cemented carbide, cermet, cubic boronitride or high speed steel,commonly have a wear resistant coating to prolong service life of thecutting tool. The wear resistant coatings are frequently coated usingCVD since this technique has several advantages. It enables largethroughput in production of the cutting tools, conformal coating oncomplex geometries and can readily be used to deposit insulating coatinglayers such as alumina.

In particular, cemented carbide cutting tools for turning are usuallycoated with CVD coatings comprising a layered structure of differentmaterials to provide sufficient wear resistance, where composition,microstructure, texture etc. of the individual layers are chosen toimprove certain properties of the coating for a specific application.The predominant coating used today comprises a Ti-based layer,hereinafter referred to as Ti(C,N,O) layer comprising one or more layersselected from titanium carbide, titanium nitride, titanium carbonitride,titanium oxycarbide and titanium oxycarbonitride, hereinafter referredto as TiC, TiN, Ti(C,N), Ti(C,O), Ti(C,N,O) layers, deposited on asurface of the substrate and an alumina layer, hereinafter referred toas Al₂O₃ layer, deposited on the Ti(C,N,O) layer. Moderate temperatureCVD (MTCVD) processes has proven to be advantageous for deposition ofTi(C,N) layers as compared to high temperature CVD (HTCVD) processes.

Larsson and Ruppi, Thin Solid Films 402 (2002) 203-210 discloses a studyon the microstructure and properties of Ti(C,N) coatings deposited oncutting tool substrates using MTCVD, as compared with Ti(C,N) coatingsdeposited using HTCVD. The HTCVD Ti(C,N) coating exhibits equiaxedgrains without preferred growth direction and an average grain size ofless than 0.2 μm. In contrast the MTCVD Ti(C,N) coatings exhibit arelatively large TC(422) value in X-ray diffraction measurement,hereinafter referred to as a (422) texture, and columnar grains having awidth of about 0.5 μm. The difference in microstructure is assigned tothe lower temperature and aggressive precursors, such as acetonitrile(CH₃CN). The MTCVD Ti(C,N) coating has better edge chipping resistance,but worse crater wear resistance, as compared to the HTCVD Ti(C,N)coating. However, flaking resistance still is critical for MTCVD Ti(C,N)coatings, in particular in demanding applications such as turning innodular cast iron comprising intermittent cutting operations.

EP 1 897 970 A1 discloses a columnar Ti(C,N) layer with a (422) texturedeposited using a MTCVD process with precursors comprising acetonitrile,titanium tetrachloride, nitrogen and hydrogen, and in addition ahydrocarbon such as C₂H₄ or C₃H₆, which is disclosed to give high atomicratio of carbon to the sum of carbon and nitrogen (C/C+N) contained inthe columnar Ti(C,N) layer, i.e. at least 0.70, and thus a high hardnessand improved wear resistance as compared to a standard acetonitrileprocess in accordance with above. The columnar Ti(C,N) layer formedusing these precursors is fine-grained with an average grain width of0.05 to 0.5 μm and has a high fracture resistance. Albeit the improvedhardness the oxidation resistance of this columnar Ti(C,N) layer may beinsufficient, in particular for cutting operations generating a lot ofheat in the coating.

SUMMARY

It is an object of the present invention to provide a coated cuttingtool with improved properties in cutting operations. It is a furtherobject of the invention to provide a coated cutting tool with improvedwear resistance, for example a higher resistance to flaking. Anotherobject of the invention is to provide a cutting tool with highperformance in milling of grey cast iron and nodular cast iron.

These objects are achieved by a cutting tool according to claim 1.Preferred embodiments are disclosed in the dependent claims.

The present invention relates to a coated cutting tool comprising asubstrate and a coating, wherein said coating comprises a Ti(C,N) layercomprising at least one columnar MTCVD Ti(C,N) layer with an averagegrain width of 0.05-0.5 μm, preferably 0.05-0.4 μm, more preferably0.05-0.25 μm, most preferably 0.1-0.2 μm, measured on a cross sectionwith a surface normal perpendicular to a surface normal of thesubstrate, on a rake face of the coated cutting tool, along a straightline in a direction parallel to a surface of the substrate, at acentered position between a lowermost and an uppermost interface of saidMTCVD Ti(C,N) layer. The atomic ratio of carbon to the sum of carbon andnitrogen (C/(C+N)) contained in said MTCVD Ti(C,N) layer is 0.50-0.65,preferably 0.52-0.60, more preferably 0.54-0.56, when measured forexample by electron microprobe analysis using a electron microprobe at10 positions spaced 50 μm along said straight line. Said MTCVD Ti(C,N)layer exhibits an X-ray diffraction pattern, as measured using CuKαradiation, wherein the texture coefficients TC(hkl) are defined as

${{TC}({hkl})} = {\frac{I({hkl})}{I_{0}\left( {hkl} \right)}\left\lbrack {\frac{1}{n}{\sum\limits_{n = 1}^{n}\frac{I({hkl})}{I_{0}({hkl})}}} \right\rbrack}^{- 1}$where I(hkl)=measured intensity (peak area) of the (hkl) reflection,I₀(hkl)=standard intensity according to ICDD's PDF-card No. 42-1489,n=number of reflections used in the calculation, (hkl) reflections usedare: (111), (200), (220), (311), (331), (420), (422) and (511), andwherein a sum of TC(422) and TC(311) is less than or equal to 5.5.

One advantage with the fine-grained MTCVD Ti(C,N) layer of the presentinvention is that it enables a smooth surface as compared to aconventional MTCVD Ti(C,N) layer. Preferably the MTCVD Ti(C,N) layer ofthe present invention may have a smoothening effect, i.e. the outersurface of the MTCVD Ti(C,N) layer has a lower surface roughness R_(Z)than the substrate surface. Another advantage with the MTCVD Ti(C,N)layer of the present invention is that the resistance to thermal crackshas been improved especially in milling applications. Another advantagewith the cutting tool in accordance with the present invention is thatthe flaking resistance is improved in milling applications.

In one embodiment of the invention an average thicknesses of saidcolumnar MTCVD Ti(C,N) layer is 2-7 μm, preferably 3-6 μm, mostpreferably 3-5 μm.

In one embodiment of the present invention the cutting tool furthercomprises an Al₂O₃ layer. The Al₂O₃ layer can be a κ-Al₂O₃ layer, anα-Al₂O₃ layer or a mixture thereof.

In one embodiment the cutting tool of the present invention comprises anα-Al₂O₃ layer that exhibits an X-ray diffraction pattern, wherein thetexture coefficients TC(hkl) can be defined as

${{TC}({hkl})} = {\frac{I({hkl})}{I_{0}\left( {hkl} \right)}\left\lbrack {\frac{1}{n}{\sum\limits_{n = 1}^{n}\frac{I({hkl})}{I_{0}({hkl})}}} \right\rbrack}^{- 1}$where I(hkl)=measured intensity (peak area) of the (hkl) reflection,I₀(hkl)=standard intensity according to ICDD's PDF-card No. 10-0173,n=number of reflections used in the calculation.

In one embodiment of the present invention the TC(104) for the α-Al₂O₃layer is >1.5, preferably >2, more preferably >3, most preferably >4,wherein the (hkl) reflections used are (104), (110), (113), (024),(116), (214), (300) and (0 0 12).

In one embodiment of the present invention the TC(110) for the α-Al₂O₃layer is >1.5, preferably >2, more preferably >3, most preferably >4,wherein the (hkl) reflections used are (104), (110), (113), (024),(116), (214), (300) and (0 0 12).

In one embodiment of the present invention the TC(113) for the α-Al₂O₃layer is >1.5, preferably >2, more preferably >3, most preferably >4,wherein the (hkl) reflections used are (104), (110), (113), (024),(116), (214), (300) and (0 0 12).

In one embodiment of the present invention the TC(024) for the α-Al₂O₃layer is >1.5, preferably >2, more preferably >3, most preferably >4,wherein the (hkl) reflections used are (104), (110), (113), (024),(116), (214), (300) and (0 0 12).

In one embodiment of the present invention the TC(116) for the α-Al₂O₃layer is >1.5, preferably >2, more preferably >3, most preferably >4,wherein the (hkl) reflections used are (104), (110), (113), (024),(116), (214), (300) and (0 0 12).

In one embodiment of the present invention the TC(0 0 12) for theα-Al₂O₃ layer is >1.5, preferably >2, more preferably >3, mostpreferably >4, wherein the (hkl) reflections used are (104), (110),(113), (024), (116), (214), (300) and (0 0 12).

In one preferred embodiment the sum of TC(104) and TC(0 0 12) for theα-Al₂O₃ layer is more than 4, preferably more than 5 and more preferablymore than 6, wherein the (hkl) reflections used are (104), (110), (113),(024), (116), (214), (300) and (0 0 12).

In one embodiment of the invention an average thickness of said α-Al₂O₃layer is 1-8 μm, preferably 2-6 μm, most preferably 3-5 μm.

In one embodiment of the present invention the coating further comprisesone or more additional layers in-between and/or thereon such as a colorlayer deposited as an outermost layer.

In one embodiment of the invention the Ti(C,N) layer further comprisesadditional layers such as for example a TiN layer serving as a diffusionbarrier deposited on the substrate prior to said MTCVD Ti(C,N) layer.Another example of an additional layer is one or more layers depositedon said MTCVD Ti(C,N) layer prior to deposition of said Al₂O₃ layer.These layers may for example provide improved adhesion of the outerlayer.

In one embodiment of the invention the Ti(C,N) layer comprises aninnermost TiN layer with a thickness enough to provide a diffusionbarrier, preferably a thickness of 0.3 to 0.6 μm.

In one embodiment of the invention the coated cutting tool furthercomprises a Ti(C,N,O) layer, a Ti(C,O) layer, a Ti(Al)(C,N,O) layer orany combination thereof as a bonding layer between the MTCVD Ti(C,N)layer and the α-Al₂O₃ layer. The bonding layer is suitably 0.5-3 μm,preferably 0.5-2 μm thick.

In one embodiment of the invention the Ti(C,N) layer comprises a HTCVDTi(C,N) layer deposited on the MTCVD Ti(C,N) layer.

In one embodiment of the invention the coating comprises a Ti(C,N) layerconsisting of a sequence of layers in accordance with TiN/MTCVDTi(C,N)/HTCVD Ti(C,N) deposited on the substrate. Preferably thethickness of the TiN layer is 0.3 μm to 0.6 μm. Preferably the thicknessof the MTCVD Ti(C,N) layer is 2-7 μm, more preferably 3-5 μm, to providesufficient resistance to abrasive flank wear. Preferably the thicknessof the HTCVD Ti(C,N) layer is 0.2 μm to 0.5 μm. The columnar grains ofthe MTCVD Ti(C,N) layer are elongated with a length and a width and witha longitudinal axis along a growth direction of the MTCVD Ti(C,N) layerbeing perpendicular to a surface of the substrate. The grain width isnot uniaxed but may differ in different directions. In addition thegrains are generally not perfectly aligned with the growth direction.Hence the grain width is not easily measured. For the purpose of thepresent application, the width of the columnar grains is considered toextend in a direction parallel to the surface of the substrate, which isin a direction perpendicular to the growth direction of the MTCVDTi(C,N) layer, and is measured in a scanning electron microscope (SEM)micrograph of a polished cross section of the MTCVD Ti(C,N) layer at amagnification of 15 000×. Grain boundaries are identified by differencesin contrast between adjacent grains and grain widths are measured as thedistance between the adjacent grain boundaries along a straight line asfurther explained in the following.

In the cutting tool according to the present invention, the MTCVDTi(C,N) layer exhibits an X-ray diffraction pattern, wherein the texturecoefficients TC(hkl) are calculated as defined above, but whereinI(hkl)=measured intensity (peak area) of the (hkl) reflection,I₀(hkl)=standard intensity according to ICDD's PDF-card No. 42-1489,n=number of reflections used in the calculation, (hkl) reflections usedare: (111), (200), (220), (311), (331), (420), (422) and (511), andwherein a sum of TC(422) and TC(311) is less than or equal to 5.5, inone embodiment less than 5, in one embodiment less than 4.5 and in oneembodiment less than 4. The sum of TC(422) and TC(311) can be more than1 but less than or equal to 5.5, or more than 1.5 but less than 5, ormore than 2 but less than 4.5, or more than 2.5 but less than 4. TC(311)is in one embodiment higher than TC(422).

In one embodiment of the present invention the MTCVD Ti(C,N) layerexhibits an X-ray diffraction pattern having the (422) reflection at a2θ position of 123.15-123.25. The 2θ position of the (422) reflectionrelates to the carbon content in the coating such that a higher carboncontent correlates to a lower 2θ position of the (422) reflection.

In one embodiment of the present invention a value of the full width athalf max (FWHM) of the peak assigned to the (422) reflection of theMTCVD Ti(C,N) layer is 0.35-0.5, preferably 0.4-0.5, most preferably0.42-0.46. The FWHM is related to the grain size such that a highervalue of the FWHM correlates to smaller grains.

In one embodiment of the present invention, the cutting tool has beensubjected to a brushing treatment of the cutting edge and/or a blastingtreatment. This is advantageous in that the flaking resistance of thecutting edge is improved.

Thanks to the improved wear resistance of the MTCVD Ti(C,N) layer thetoughness of the substrate can be increased at the expense of hardness.In one embodiment of the present invention the substrate is made ofcemented carbide comprising WC grains in a binder phase comprising Co.Preferably the Co content is 5.5-10 wt-%, preferably 6-8 wt-%.

Although embodiments of the present invention have been described withTi as the only metal element in the Ti(C,N) layer, Ti(C,N) layer orindividual layers thereof in addition to Ti may comprise elementsselected from one or more of Zr, Hf, V, Nb, Ta, Cr, Mo, W and Al in anamount not significantly altering the grain width or C/(C+N) ratio ofthe MTCVD Ti(C,N) layer. Moreover, the Ti(C,N) layer may also compriseB. Moreover, said MTCVD Ti(C,N) layer may comprise small amounts ofoxygen without having significant effect on the properties of the MTCVDTi(C,N) layer. In one embodiment of the invention the Ti(C,N) layercomprises one or more of these additional elements.

Although the α-Al₂O₃ layer is described as a binary compound layer itshould be appreciated that in alternative embodiments of the inventionthe Al₂O₃ layer may comprise one or more further elements such as forexample Zr to form a ternary or a multinary compound such as (Al,Zr)O.

One advantage of the invention is that a small grain width in the MTCVDTi(C,N) layer can be provided without having excessive amount of carbonin the process or in the coating layers formed.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings andclaims.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a coating in accordance with oneembodiment of the invention, made in accordance with Example 1,

FIG. 2 is a cross sectional view of a Ti(C,N) coating representing priorart, made in accordance with Example 2,

FIG. 3 is a cross sectional view of a Ti(C,N) coating in accordance withone embodiment of the present invention made in accordance with Example3,

FIG. 4 is a LOM image of the edge line of a cutting tool (Sample 1A) inaccordance with one embodiment of the invention tested in accordancewith Example 4,

FIG. 5 is a LOM image of the edge line of a cutting tool (Sample 2A) inaccordance with prior art tested in accordance with Example 4,

FIG. 6 is a LOM image of the edge line of a cutting tool (Sample 3A) inaccordance with one embodiment of the invention tested in accordancewith Example 4,

FIG. 7 is a LOM image of the edge line of a cutting tool (Sample 1A) inaccordance with one embodiment of the invention tested in accordancewith Example 5,

FIG. 8 is a LOM image of the edge line of a cutting tool (Sample 2A) inaccordance with prior art tested in accordance with Example 5, and

FIG. 9 is a LOM image of the edge line of a cutting tool (Sample 3A) inaccordance with one embodiment of the invention tested in accordancewith Example 5.

DETAILED DESCRIPTION

Coated cutting tools in accordance with embodiments of the presentinvention were manufactured as disclosed in Example 1 and Example 3,comprising a here called “fine-grained” MTCVD Ti(C,N) and an α-Al₂O₃layer. These coated cutting tools were compared to coated cutting toolsmade in accordance with prior art, Example 2, comprising coarser grainedMTCVD Ti(C,N) and an α-Al₂O₃ layer corresponding to the α-Al₂O₃ layer inExample 3. Cross sectional views of the Ti(C,N layer as deposited inaccordance with Example 3 are shown in FIG. 3 and in accordance withExample 2 shown in FIG. 2 .

The comparing is based on performance tests as disclosed in Example 4and Example 5. The coating deposition parameters are shown in Table 1and Table 2, the as measured coating thicknesses in Table 3, the texturecoefficients of the Ti(C,N) layer are disclosed in Table 4 and thetexture coefficients of the α-Al₂O₃ layer are disclosed in Table 5.

EXAMPLE 1 Invention

Coated cutting tools in accordance with one embodiment of the inventionwere manufactured. First, cemented carbide R365-1505ZNE-KM substrateswere manufactured. The substrates were then coated in a depositionprocess as disclosed in Table 1.

Substrates with a composition of 7.61 wt % Co, 1.15 wt % Ta, 0.27 wt %Nb and balance WC, a Hc value of 14.5 kA/m (measured using a FoersterKoerzimat CS1.096 according to DIN IEC 60404-7) and a hardness HV3 of1550 GPa were manufactured by pressing powder and sintering the pressedbodies. Prior to deposition the substrates were edge rounded to about 35μm by wet blasting. A coating consisting of first a Ti(C,N) layer with atotal thickness of about 4.8 μm, which consists of the layer sequence0.3 μm TiN, 4.1 μm MTCVD Ti(C,N) and 0.4 μm HTCVD Ti(C,N), then a 0.8 μmbonding layer of Ti(C,N,O), and an α-Al₂O₃ layer with a thickness of 3.7um and finally a 1.2 μm thick color layer of TiN/TiC/TiN/TiC/TiN wasdeposited by CVD on the substrates. The coating was deposited in a CVDreactor having radial gas flow using deposition conditions for growth ofthe layers as described in Table 1.

After the deposition the coated cutting tools some of the tools weresubjected to blasting and some were subjected to edge line brushingprior to the performance testing. In the following samples called Sample1A were subjected to wet blasting to remove the color layers on the rakefaces, and coated cutting tools called Sample 1B were subjected to edgeline brushing to homogenize the coating on the edge line.

FIG. 1 shows a cross-sectional SEM image of the coating and theoutermost part of the substrate on the rake face of one of the coatedcutting tools at a magnification of 15 000×. The MTCVD Ti(C,N) layer hasa columnar structure with fine columnar grains. In order to evaluate thegrain size of the MTCVD Ti(C,N) layer the grain width was measured inthe SEM and further explained below. The average grain width was 140 nm.

Texture coefficients TC (hkl) of the columnar grains of the MTCVDTi(C,N) layer, see Table 4, and the α-Al₂O₃ layer, see Table 5, weredetermined by X-ray diffraction, as explained in detail below. The MTCVDTi(C,N) shows a sum of TC(311) and TC(422) that is 3.92. TheX-Ray-diffraction measurement of the α-Al₂O₃ layer shows that the sum ofTC(0 0 12) and TC(104) is 5.98.

The MTCVD Ti(C,N) layer exhibits an X-ray diffraction pattern having thepeak of the (422) reflection at 2θ=123.3°, which has been determined asexplained in the following. This peak position corresponds to a C/(C+N)ratio in the MTCVD Ti(C,N) layer of 0.55. A second method used todetermine the carbon content by X-Ray diffraction is by using Rietveldrefinement. The result from this approach is the same as the result frompeak position. The FWHM of the peak of the (422) reflection is 0.37°.

EXAMPLE 2 Prior Art

Coated cutting tools representing prior art were manufactured to serveas references. The deposition conditions for growth of the coatings aredescribed in Table 2. A cross sectional view of the deposited Ti(C,N) isshown in FIG. 2 .

First, cemented carbide R365-1505ZNE-KM substrates with the samecomposition as disclosed in Example 1 above were manufactured. Prior tocoating deposition the substrates were edge rounded to about 35 μm bywet blasting. A coating consisting of the layer sequence 0.3 μm TiN, 4.7μm MTCVD Ti(C,N), 0.4 μm HTCVD Ti(C,N), 0.6 μm bonding layer comprisingTi(C,O), an α-Al₂O₃ layer with a thickness of about 3.4 μm and a 1.4 μmTiN/TiC/TiN/TiC/TiN color layer was deposited by CVD on the substrates.

After deposition the coated cutting tools called Sample 2A weresubjected to wet blasting to remove the color layer on the rake faces,and coated cutting tools called Sample 2B were subjected to edge linebrushing to homogenize the coating on the edge line.

Texture coefficients TC (hkl) of the columnar grains of the MTCVDTi(C,N) layer, see Table 4, and the α-Al₂O₃ layer, see Table 5, weredetermined by X-ray diffraction, as explained in detail below. The MTCVDTi(C,N) has a sum of TC(311) and TC(422) that is 3.85. TheX-Ray-diffraction measurement of the α-Al₂O₃ layer shows that the sum ofTC(0 0 12) and TC(104) is 2.6.

The MTCVD Ti(C,N) layer exhibits an X-ray diffraction pattern having thepeak of the (422) reflection at 2θ=123.47°, which has been determined asexplained in the following. This peak position corresponds to a C/(C+N)ratio in the MTCVD Ti(C,N) layer of 0.52. The FWHM of the peak of the(422) reflection is 0.27°.

EXAMPLE 3 Invention

Coated cutting tools were manufactured in accordance with Example 1 withthe corresponding MTCVD Ti(C,N) layer but with a bonding layer, anα-Al₂O₃ layer and a color layer corresponding to Example 2, as shown inTable 1 and 2. A cross sectional view of the deposited Ti(C,N) is shownin FIG. 3 .

Texture coefficients TC (hkl) of the columnar grains of the MTCVDTi(C,N) layer, see Table 4, and the α-Al₂O₃ layer, see Table 5, weredetermined by X-ray diffraction, as explained in detail below. The MTCVDTi(C,N) has a sum of TC(311) and TC(422) that is 3.84. TheX-Ray-diffraction measurement of the α-Al₂O₃ layer shows that the sum ofTC(0 0 12) and TC(104) is 2.17.

After deposition the coated cutting tools called Sample 3A weresubjected to wet blasting to remove the color layer on the rake faces,and coated cutting tools Sample 3B were subjected to edge line brushingto homogenize the coating on the edge line.

TABLE 1 Color layer MTCVD HTCVD HTCVD TiN/TiC/TiN/TiC/TiN TiN Ti(C, N)Ti(C, N) Ti(C, N) α-Al₂O₃ Ex. 1 Ex. 1, 3 Ex. 1, 3 Ex. 1 Ex. 3 Ex. 1 TiNTiC Precursors Vol-% Vol-% Vol-% Vol-% Vol-% Vol-% Vol-% H₂ 60.20 96.6067.89 76.93 90.70 49.14 93.29 N₂ 38.30 — 25.46 15.38 — 49.14 — CH₄ — —3.39 5.13 — — 4.19 HCl — — 1.70 — 2.91 — — CO — — — — — — — TiCl₄ 1.502.95 1.56 2.56 — 1.72 2.52 CH₃CN — 0.45 — — — — — CO₂ — — — — 4.65 — —H₂S — — — — 0.58 — — AlCl₃ — — — — 1.16 — — Temperature (° C.) 930 8301000 1010 1000 1000 1000 Pressure (mbar) 160 80 400 55 55 atm atm Ti/CNratio — 6.6 — — — — —

TABLE 2 Color layer MTCVD HTCVD TiN/TiC/TiN/TiC/TiN TiN Ti(C, N) Ti(C,N) α-Al₂O₃ Ex. 2, 3 Ex. 2 Ex. 2 Ex. 2 Ex. 2, 3 TiN TiC Precursors Vol-%Vol-% Vol-% Vol-% Vol-% Vol-% H₂ 60.20 82.25 76.93 82.97 49.14 93.29 N₂38.30 7.83 15.38 49.14 — CH₄ — — 5.13 — 4.19 HCl — 7.83 — 5.49 — — CO —— — — — TiCl₄ 1.50 1.44 2.56 1.72 2.52 CH₃CN — 0.65 — — — CO₂ — — — 8.79— — H₂S — — — 0.55 — — AlCl₃ — — — 2.20 — — Temperature (° C.) 930 8851010 1010 1010 1010 Pressure (mbar) 160 55 55 55 atm atm Ti/CN ratio —2.2 — — — —

TABLE 3 Coating MT CVD HT CVD Bonding Decorative thickness TiN Ti(C, N)Ti(C, N) layer α-Al₂O₃ layer Total Ex. 1 0.3 4.1 0.4 0.8 3.7 1.2 10.5Ex. 2 0.3 4.7 0.4 0.6 3.4 1.4 10.8 Ex. 3 0.3 5.3 0.4 0.6 3.3 1.3 11.2

TABLE 4 MTCVD TC(311) + Ti(C, N) TC(111) TC(200) TC(220) TC(311) TC(331)TC(420) TC(422) TC(511) TC(422) Ex. 1 1.53 0.24 0.64 3.08 0.51 0.72 0.840.44 3.92 Ex. 2 0.87 0.15 1.21 2.32 0.83 0.72 1.53 0.37 3.85 Ex. 3 1.190 0.71 1.97 1.15 0.60 1.87 0.51 3.84

TABLE 5 TC(104) + α-Al₂O₃ TC(104) TC(110) TC(113) TC(024) TC(116)TC(214) TC(300) TC(0 0 12) TC(0 0 12) Ex. 1 3.84 0.32 0.24 0.39 1.08 0 02.14 5.98 Ex. 2 2.60 1.08 0.97 0.83 1.24 0.72 0.55 0 2.6 Ex. 3 2.17 0.801.11 1.35 1.68 0.51 0.38 0 2.17

EXAMPLE 4 Flaking Test

Coated cutting tools of Example 1, 2 and 3 were tested in face millingof a 120 mm wide component of nodular cast iron SS0727, without coolantunder the following conditions.

Cutting speed, V_(c) 300 m/min Feed, f_(z) 0.3 mm/rev Depth of cut,a_(p) 3 mm No. of teeth 1 Diameter of cutter 160 mm Width of cut formilling, a_(e) 120 mm

One pass of the test piece was cut and thereafter the wear of thecutting edge of each tool was studied in a light optical microscope. Theintermittent dry cutting of nodular cast iron is a demanding cuttingoperation and flaking often limit the tool life.

The Samples 1A that had been subjected to blasting showed the bestflaking resistance, better than the Samples 2A and 3A. Andcorrespondingly the Sample 1B that had been subjected to brushing of theedge line showed a better flaking resistance than the Samples 2B and 3B.The blasted samples showed an increased resistance to flaking ascompared to the edge line brushed samples 1B-3B. SEM images of testedcutting tools are shown in FIG. 4-6 , wherein Sample 1A is shown in FIG.4 , sample 2A is shown in FIG. 5 and sample 3A is shown in FIG. 6 .

EXAMPLE 5 Thermal Cracks

Coated cutting tools of Example 1, 2 and 3 were tested in face millingof a 120 mm wide component of grey cast iron (SS0125) with coolant

Cutting speed, V_(c) 220 m/min Feed, f_(z) 0.25 mm/rev Depth of cut,a_(p) 3 mm No. of teeth 1 Diameter of cutter 160 mm Width of cut formilling, a_(e) 60 + 60 mm The cutter is placed centrally in the 2^(nd)cut

Six passes were run with the same cutting edge of each tool. The cuttingtools are subjected to a high degree of thermal cycling in this test dueto the intermittent machining and use of coolant, which can causethermal cracks extending across the cutting edge. As a consequence offormed thermal cracks, also called comb cracks, the edge mighteventually suffer from chipping whereby portions of the coating and thesubstrate spall off.

FIG. 7-9 shows light optical microscope (LOM) images of the edge line ofthe cutting tools after the test of Example 5 of Samples 1A, 2A and 3A,respectively.

The coated cutting tools in accordance with Samples 2A and 2B sufferedfrom flaking, while all the cutting tools of Sample 1A, 1B, 3A and 3Bdeveloped fewer and smaller cracks. Since the cutting tools made inaccordance with Example 1 (Sample 1A, 1B) and Example 3 (Sample 3A, 3B)comprises the corresponding MTCVD Ti(C,N) layer representing embodimentsof the present invention, while the cutting tools of Example 2 comprisesan MTCVD Ti(C,N) representing prior art, a resistance to thermal crackformation in the present test is considered to be related to theproperties of the MTCVD Ti(C,N) layer in accordance with the presentinvention.

For the purpose of the present application, and in particular for theabove examples, methods for determining properties of the coatings aredefined in the following.

In order to evaluate the thicknesses and grain size of individual layersof the coating the coated cutting tool is cut, ground and polished toobtain a polished cross section with a surface normal perpendicular to asurface normal of the substrate on the rake face of the coated cuttingtool.

The layer thicknesses are measured using a light optical microscope(LOM).

In order to enable grain width measurement it is necessary to obtain asmooth surface that gives sufficient contrast between grains ofdifferent orientation in the MTCVD Ti(C,N) layer by electronchannelling. Thus for the purpose of grain width measurement thepolishing of the cross section comprises the steps of:

-   -   rough polishing on paper using an oil-based diamond suspension        (from Microdiamant AG) with an average diamond particle size of        9 μm and 0.7 g of diamond particles per 2 dl oil (Mobil Velocite        no. 3),    -   fine polishing on paper using an oil-based diamond suspension        (from Microdiamant AG) with an average diamond particle size of        1 μm and 0.7 g of diamond particles per 2 dl oil (Mobil Velocite        no. 3), and    -   oxide polishing using a soft cloth and under dripping of a        suspension comprising a mixture of SiO₂ (10-30%) and Al₂O₃        particles (1-20%) with average particle size of 0.06 μm        (Masterpolish 2, Buehler) at 150 rev/min and pressure 35 N for        220 s.

The grain width was measured from a SEM micrograph of the polished crosssection at a magnification of 15 000× in the SEM obtained at 5.0 kV andworking distance 5 mm. The grain boundaries are identified bydifferences in contrast between adjacent grains and grain widths aremeasured as the distance between the identified adjacent grainboundaries along a 10 μm straight line in a direction parallel to asurface of the substrate, at a centered position between a lowermost andan uppermost interfacial surface of the MTCVD Ti(C,N) layer. Grainwidths smaller than 20 nm are not readily identified in the SEM imageand are not considered.

The columnar MTCVD Ti(C,N) layer comprises twinned columnar grains andmay comprise even other intergranular defects or dislocations, which arenot intended to be counted as grain boundaries in this method. Twinboundaries may be identified and excluded since the symmetry andorientation of the twin grains may not generate any substantialdifference in contrast when passing the twin boundaries. Hence, thetwinned columnar grain is intended to be treated as one grain whendetermining the grain width.

In order to investigate the texture coefficients of the MTCVD Ti(C,N)layer X-Ray diffraction is conducted on the flank face using aPANalytical CubiX³ diffractometer equipped with a PIXcel detector. Thecoated cutting tools are mounted in sample holders that ensure that theflank face of the samples are parallel to the reference surface of thesample holder and also that the flank face is at appropriate height.Cu-K_(α) X-rays are used for the measurements, with a voltage of 45 kVand a current of 40 mA. Anti-scatter and slits of ½ degree anddivergence slit of ¼ degree are used. The diffracted intensity from thecoated cutting tool is measured around 2θ angles were TiCN peaks occur,ranging from approximately 20° to 140°, i.e. over an incident angle θrange from 10 to 70°.

Data analysis, including background subtraction and Cu-K_(α) stripping,is performed using PANalytical's X'Pert HighScore software, andintegrated peak areas emanating from this are used to calculate thetexture coefficients TC (hkl) of the MTCVD Ti(C,N) layer using X'PertIndustry software by comparing the ratio of the measured intensity datato standard intensity data according to

${{TC}({hkl})} = {\frac{I({hkl})}{I_{0}\left( {hkl} \right)}\left\lbrack {\frac{1}{n}{\sum\limits_{n = 1}^{n}\frac{I({hkl})}{I_{0}({hkl})}}} \right\rbrack}^{- 1}$where I(hkl)=measured area intensity of the (hkl) reflection,I₀(hkl)=standard intensity according to ICDD's PDF-card no 42-1489,n=number of reflections used in the calculation, (hkl) reflections usedare: (111), (200), (220), (311), (331), (420), (422) and (511).

Since the MTCVD Ti(C,N) layer is a finitely thick film the relativeintensities of a pair of peaks of the same compound are different thanthey are for bulk samples, due to the differences in path length throughthe Ti(C,N) layer. Therefore, thin film correction is applied to theintegrated peak area intensities, taken into account also the linearabsorption coefficient of Ti(C,N), when calculating the TC values. Sincethe substrates used in the examples were WC a further correction isapplied to correct for the overlap of the TiCN (311) by the WC (111)peak. This is made by deducting 25% of the area intensity of another WCpeak, namely WC(101) from the TiCN (311) area intensity. Since possiblefurther layers above the MTCVD Ti(C,N) layer will affect the X-rayintensities entering the MTCVD Ti(C,N) layer and exiting the wholecoating, corrections need to be made for these as well, taken intoaccount the linear absorption coefficient for the respective compound ina layer.

In order to estimate the carbon content the diffraction angle 2θ of the(422) reflection in the X-ray diffraction pattern obtained using CuK_(α)radiation is determined. The position of the (422) reflection relates tothe carbon content in the coating such that a higher carbon contentcorrelates to a lower angle of the (422) reflection. The C/N ratio, inthe interval from TiC₀N₁ to TiC₁N₀, shows a linear dependence to thediffraction angle 2θ, making it possible to extract information aboutthe C/N ratio by measuring the position of the (422) reflection.

A second method used to determine the carbon content is by usingRietveld refinement to the complete diffraction pattern collected asdiscussed above. From the refinement it is possible to extract data onlattice parameters for the TiCN phase. The lattice parameter also varieslinearly with the C/N ratio as discussed above. The result from thisapproach correlates well with the results where the diffraction anglewas the parameter used to probe the carbon content.

The (422) reflection is also used to estimate the grain width. This isaccomplished by determining the FWHM of the peak in the diffractogram.The FWHM is related to the grain size such that a higher value of thewidth correlates to smaller grains.

Elemental analysis is performed by electron microprobe analysis using aJEOL electron microprobe JXA-8900R equipped with wavelength dispersivespectrometers (WDS) in order to determine the C/(C+N) ratio of the MTCVDTi(C,N) layer. The analysis of the MTCVD Ti(C,N) layer averagecomposition is conducted on a polished cross section on the flank facewithin the MTCVD Ti(C,N) layer in 10 points with spacing of 50 μm alonga straight line in a direction parallel to a surface of the substrate,at a centered position between a lowermost and an uppermost interfacialsurface of the MTCVD Ti(C,N) layer using 10 kV, 29 nA, a TiCN standard,and with corrections for atomic number, absorption and fluorescence. InExample 1 the points were placed within the MTCVD Ti(C,N) coating at adistance of 2-3 μm from the interface between the substrate and theMTCVD Ti(C,N) layer.

In order to investigate the texture coefficients of the α-Al₂O₃ layerX-Ray diffraction is conducted on the flank face. The testing isperformed on a PANalytical CubiX³ diffractometer equipped with a PIXceldetector. The samples are mounted in sample holders that ensure that aflat face, for example a flat flank face, of the samples are parallel tothe reference surface of the sample holder and also that the samplesurface is at the correct height. Cu-K_(α) X-rays are used for themeasurements, with a voltage of 45 kV and a current of 40 mA. Theirradiated area of the sample is selected to avoid a spill-over of theX-ray beam over the coated face of the sample. On the primary side afixed anti-scatter slit of ½ degree and a fixed divergence slit of ¼degree is used. On both incident and diffracted beam path soller slitsof 0.04 rad are mounted. The diffracted intensity from the sample ismeasured around 2θ angles where alpha Al₂O₃ peaks occur, ranging fromapproximately 20 to 140° (that is to say over an incident angle θ rangefrom 10 to 70°) and collected and stored by the computer attached to thediffractometer after measurement. The data collection software isPANalytical's X'Pert Industry and this software is able to internallycommunicate with the analysis software X'Pert HighScore.

In order to investigate the texture of the alpha Al₂O₃ layer X-Raydiffraction is conducted using CuK_(α) radiation and texturecoefficients TC (hkl) for different growth directions of the columnargrains of the alpha Al₂O₃ layer are calculated according to

${{TC}({hkl})} = {\frac{I({hkl})}{I_{0}\left( {hkl} \right)}\left\lbrack {\frac{1}{n}{\sum\limits_{n = 1}^{n}\frac{I({hkl})}{I_{0}({hkl})}}} \right\rbrack}^{- 1}$where I(hkl)=measured (peak integrated area) intensity of the (hkl)reflection, I₀(hkl)=standard intensity according to ICDD's PDF-card no10-0173, n=number of reflections to be used in the calculation. In thiscase the (hkl) reflections used are: (104), (110), (113), (024), (116),(214), (300) and (0 0 12).

The data analysis, including background subtraction and Cu-K_(α)stripping, is done using PANalytical's X'Pert HighScore software. Theoutput from this program are then used to calculate the texturecoefficients of the alpha Al₂O₃ in the X'Pert Industry software bycomparing the ratio of the measured intensity data to the standardintensity data (ICDD's PDF-card no 10-0173), using Eq. 1. Since thealpha Al₂O₃ layer is a finitely thick film the relative intensities of apair of peaks at different 2θ angles are different than they are forbulk samples, due to the differences in path length through the alphaAl₂O₃ layer. Therefore, thin film correction is applied to theintegrated peak area intensities, taken into account also the linearabsorption coefficient of alpha Al₂O₃, when calculating the TC values.Since possible further layers above the alpha Al₂O₃ layer will affectthe X-ray intensities entering the alpha Al₂O₃ layer and exiting thewhole coating, corrections need to be made for these as well, taken intoaccount the linear absorption coefficient for the respective compound ina layer. Alternatively, a further layer such as TiN above an aluminalayer can be removed by a method that does not substantially influencethe XRD measurement results, e.g. etching.

While the invention has been described in connection with variousexemplary embodiments, it is to be understood that the invention is notto be limited to the disclosed exemplary embodiments, on the contrary,it is intended to cover various modifications and equivalentarrangements within the appended claims.

The invention claimed is:
 1. A coated cutting tool comprising: asubstrate; a surface coating disposed on the substrate, wherein saidcoating includes a Ti(C,N) layer comprising at least one columnar MTCVDTi(C,N) layer with an average grain width of 0.05-0.5μm, measured on across section with a surface normal perpendicular to a surface normal ofthe substrate, on a rake face of said coated cutting tool, along astraight line in a direction parallel to a surface of the substrate, ata centered position between a lowermost and an uppermost interface ofsaid columnar MTCVD Ti(C,N) layer, an atomic ratio of carbon to the sumof carbon and nitrogen (C/(C+N)) contained in said MTCVD Ti(C,N) layeris in average 0.50-0.65, wherein said MTCVD Ti(C,N) layer exhibits anX-ray diffraction pattern, as measured using CuKα radiation, wherein thetexture coefficients TC(hkl) are defined as${{TC}({hkl})} = {\frac{I({hkl})}{I_{0}\left( {hkl} \right)}\left\lbrack {\frac{1}{n}{\sum\limits_{n = 1}^{n}\frac{I({hkl})}{I_{0}({hkl})}}} \right\rbrack}^{- 1}$where I(hkl) =measured intensity (peak area) of the (hkl) reflection,I₀(hkl)=standard intensity according to ICDD's PDF-card No. 42-1489,n=number of reflections used in the calculation, (hkl) reflections usedare: (111),(200),(220),(311),(331),(420),(422)and (511), and a sum ofTC(422) and TC(311) is less than or equal to 5.5; and an Al₂O₃ layerdeposited above said Ti(C,N,O) Ti(C,N) layer.
 2. The coated cutting toolaccording to claim 1, wherein the average grain width is 0.1-0.2μm. 3.The coated cutting tool according to claim 1, wherein the C/(C+N) ratiois 0.54-0.56.
 4. The coated cutting tool according to claim 1, whereinan average thicknesses of said columnar MTCVD Ti(C,N) layer is 2-7μm. 5.The coated cutting tool according to claim 4, wherein said Al₂O₃ layeris an α-Al₂O₃ layer that exhibits an X-ray diffraction pattern, asmeasured using CuKαradiation, wherein the texture coefficients TC(hkl)are defined as${{TC}({hkl})} = {\frac{I({hkl})}{I_{0}\left( {hkl} \right)}\left\lbrack {\frac{1}{n}{\sum\limits_{n = 1}^{n}\frac{I({hkl})}{I_{0}({hkl})}}} \right\rbrack}^{- 1}$where I(hkl) =measured intensity (peak area) of the (hkl) reflectionI₀(hkl)=standard intensity according to ICDD's PDF-card No. 10-0173n=number of reflections used in the calculation.
 6. The coated cuttingtool according to claim 5, wherein the TC(104) for the α-Al₂O₃ layer ishigher than 1.5, when the (hkl) reflections used are (104), (110),(113), (024), (116), (214), (300) and (0 0 12).
 7. The coated cuttingtool according to claim 5, wherein the TC(110) for the α-Al₂O₃ layer ishigher than 1.5, when the (hkl) reflections used are (104), (110),(113), (024), (116), (214), (300) and (0 0 12).
 8. The coated cuttingtool according to claim 5, wherein the TC(024) for the α-Al₂O₃layer ishigher than 1.5, when the (hkl) reflections used are (104), (110),(113), (024), (116), (214), (300) and (0 0 12).
 9. The coated cuttingtool according to claim 5, wherein the TC(116) for the α-Al₂O₃ layer ishigher than 1.5, when the (hkl) reflections used are (104), (110),(113), (024), (116), (214), (300) and (0 0 12).
 10. The coated cuttingtool according to claim 5, wherein the TC(0 0 12) for the α-Al₂O₃ layeris higher than 1.5, when the (hkl) reflections used are (104), (110),(113), (024), (116), (214), (300) and (0 0 12).
 11. The coated cuttingtool according to claim 5, wherein the sum of TC(104) and TC(0 0 12) forthe α-Al₂O₃ layer is higher than 4, when the (hkl) reflections used are(104), (110), (113), (024), (116), (214), (300) and (0 0 12).
 12. Thecoated cutting tool according to claim 1, wherein the Al₂O₃ layer has anaverage thickness of 1-8μm.
 13. The coated cutting tool according toclaim 1, wherein the insert has been subjected to a brushing treatmentof the cutting edge and/or a blasting treatment.
 14. The coated cuttingtool according to claim 1, wherein an average thicknesses of saidcolumnar MTCVD Ti(C,N) layer is 3-5μm.
 15. The coated cutting toolaccording to claim 1, wherein the Al₂O₃ layer has an average thicknessof 2-6μm.
 16. The coated cutting tool according to claim 1, wherein theAl₂O₃ layer has an average thickness of 3-4μm.